This is a very different situation in quite a few ways. For one, IE was not just a big browser, but was almost completely dominant. For another, many of IE's browser-specific features were Windows-only by design, such as ActiveX.

Here, we have an open source rendering engine that clearly delineates browser-specific features (each of which is well-documented). The use of a prefix makes it possible to use the browser-specific features offered by WebKit without sacrificing compatibility with other browsers, something Microsoft actively resisted. For quite a while, it was very difficult, if not impossible, to make sites that looked and felt right both in IE and in other browsers.

Had Microsoft extended standards in a way that played nice with the rest of the community, maybe they would have had someone saying something like this in their defence. Instead, they used browser-specific features as a way of undermining standards.